Mode softening and phononic-crystal-like behavior of FeSe

Abstract

We present a first-principles pseudopotential study on lattice dynamics of binary iron-based superconductor FeSe in both tetragonal nonmagnetic (NM) phase and orthorhombic striped antiferromagnetic (SAF) phase. It is found that significant softening of phonon modes induced by spin-phonon coupling in FeSe may increase the electron-phonon coupling strength. Moreover, we discover and report that an evident phononic-crystal-like behavior exists in FeSe, exhibiting absolute frequency gap in the range of 187 cm−1 < ω < 210 cm−1 in SAF phase, may manipulate and control phonon propagation, and have good application foreground.